1. Field of Invention
The invention relates to telecommunications networks, and more particularly to advanced architectures for telephone networks.
2. Description of Related Art
The incremental, feature by feature extension of the calling features available to users of the telephone network has given rise to the well known feature-interaction problem. As new options are added to the suite of call choices it becomes increasingly difficult to manage the behavioral complexity of the features and their resulting interactions. For instance, a telephone subscriber may subscribe to call waiting, caller ID and 3-way calling features. What happens to that subscriber when a 3-way call is made, then interrupted by a call waiting signal, can be problematic. Redesign of old telephony features to fit smoothly with the range of new features is usually not a practical option. Eventually the resulting patchwork complexity damages the quality and productivity of all phases of telecommunications service and development. It is actually the case that if not for special layers of monitoring software that examine the states of local office switching systems (such as commercially available 5ESS) and compensate for errors, the mean time between failure in those switching systems would be measured in hours, rather than months or years.
The inventors themselves in earlier work have analyzed telephone systems and their burgeoning feature sets in terms of a general decomposition into a connection specification and specifications of each user interface (P. Zave and M. Jackson, “Requirements for Telecommunications Services: An Attack on Complexity”, Proceedings of 3rd (BEE International Symposium on Requirements Engineering, IEEE Computer Society Press, pages 106-117, 1997). Each of those specifications aimed to allow for composition of the behavior due to each feature that could be relevant to the specification. That approach proved difficult, the fundamental difficulty lying in the complexity of combining the feature behaviors within each specification, and the difficulty of finding mechanisms that could handle that complexity.
Other approaches in the art trying to manage feature interactions have rested on an architectural foundation, for instance those described in J. M. Duran and J. Visser, “International Standards for Intelligent Networks”, IEEE Communications XXX(2):34-42, February 1992; J. J. Garrahan, P. A. Russo, K. Kitami and R. Kung, “Intelligent Network Overview”, IEEE Communications XXXI(3):30-36, March 1993; and J. Kamoun, “Formal Specification and Feature Interaction Detection in the Intelligent Network”, Chapter 2, Department of Computer Science, University of Ottawa, Ottawa, Ontario, 1996.
In these approaches the applied architecture is that of the “Intelligent Network”, or something closely related to it, which is a conceptual model oriented towards two-party calls. Features such as conferencing, call multiplexing, call queuing and others which connect or relate more than two parties present serious difficulties for such a conceptual model. Other architecture-based approaches known in the art include those reflected in I. Zibman, C. Woolf, P. O'Reilly, L. Strickland, D. Willis and J. Visser, “Minimizing Feature Interactions: An Architecture and Processing Model Approach” in K. E. Cheng and T. Ohta, editors, Feature Interactions in Telecommunications Systems III, IOS Press, Amsterdam, 1995, pages 65-83; M. Weiss and T. Gray, “Experiences with a Service Environment for Distributed Multimedia Applications” in P. Dini, R. Boutaba, and L. Logrippo, editors, Feature Interactions in Telecommunication Networks IV, IOS Press, Amsterdam, 1997, pages 242-253; W. J. Barr, T. Boyd and Y. Inoue, “The TINA Initiative”, IEEE Communications XXXI(3): 70-76, March 1993; and N. D. Griffith and H. Velthuijsen, “The Negotiating Agents Approach to Runtime Feature Interaction Resolution” in L. G. Bouma and H. Velthuijsen, editors, Feature Interactions in Telecommunications Systems, IOS Press, Amsterdam, 1994, pages 217-235. In the latter known approaches the analytic architecture is more flexible than the Intelligent Network, being based on agents that interact by sending messages to each other as needed. Agents may model users, resources, connections and services; or, more abstractly, may negotiate on behalf of interested parties. In some cases, both styles of representation may be used.
In most of the known approaches call features are not regarded as first-class distinct components in the architecture. That idea however is found in other known approaches, for instance reflected in K. H. Braithwaite and J. M. Atlee, “Towards Automated Detection of Feature Interactions” in L. G. Bouma and H. Velthuijsen, editors, Feature Interactions in Telecommunications Systems, IOS Press, Amsterdam, 1994, pages 36-59; and K. P Pomakis and J. M. Atlee, “Reachability Analysis of Feature Interactions: A Progress Report”, Proceedings of the International Symposium on Software Testing and Analysis, 216-223, January 1996, which characterize a feature as a stacked finite-state machine, in which the stack levels correspond to feature priority.
Other characterizations of telecommunication call features are also known in the art. In T. Ohta and Y. Harada, “Classification, Detection and Resolution of Service Interactions in Telecommunication Services” in L. G. Bouma and H. Velthuijsen, editors, Feature Interactions in Telecommunications Systems, IOS Press, Amsterdam, 1994, pages 60-72; and A. Gammelgaard and J. E. Kristensen, “Interaction Detection, a Logical Approach” in L. G. Bouma and H. Velthuijsen, editors, Feature Interactions in Telecommunications Systems, IOS Press, Amsterdam, 1994, pages 178-196, a feature is defined as a set of state-transition rules. In J. G. Thistle, R. P. Malhame, H.-H. Hoang, and S. Lafortune, “Feature Interaction Modelling, Detection and Resolution: A Supervisory Control Approach” in P. Dini, R. Boutaba, and L. Logrippo, editors, Feature Interactions in Telecommunication Networks IV, IOS Press, Amsterdam, 1997, pages 93-107, a feature is represented as a finite-state machine subject to supervisory control.
In M. Faci and L. Logrippo, “Specifying Features and Analyzing Their Interactions in a LOTOS Environment” in L. G. Bouma and H. Velthuijsen, editors, Feature Interactions in Telecommunications Systems, IOS Press, Amsterdam, 1994, pages 136-151; and K. E. Cheng, “Towards a Formal Model for Incremental Service Specification and Interaction Management Support” in L. G. Bouma and H. Velthuijsen, editors, Feature Interactions in Telecommunications Systems, IOS Press, Amsterdam, 1994, pages 152-166, a feature is a process in a process algebra. In J. Blom, B. Jonsson and L. Kempe, “Using Temporal Logic for Modular Specification of Telephone Services” in L. G. Bouma and H. Velthuijsen, editors, Feature Interactions in Telecommunications Systems, IOS Pros, Amsterdam, 1994, pages 197-216; and P. Combes and S. Pickin, “Formalization of a User View of Network and Services for Feature Interaction Detection” in L. G. Bouma and H. Velthuijsen, editors, Feature Interactions in Telecommunications Systems, IOS Press, Amsterdam, 1994, pages 120-135, a feature is a set of rules in a temporal logic. F. J. Lin and Y. J. Lin, “A Building Block Approach to Detecting and Resolving Feature Interactions” in L. G. Bouma and H. Velthuijsen, editors, Feature Interactions in Telecommunications Systems, IOS Press, Amsterdam, 1994, pages 86-119, also regard features as distinct components to be configured according to architectural constraints.
However, none of the known approaches to network feature management or specification effectively manage the basic feature interaction problem in the telephone network. A systematic approach for telephone network architecture which effectively and reliably manages all the permutations of call features, current and future, is fundamentally desirable.